Update Coveralls GitHub Actions integration

[devin-ai-integration]

Update Coveralls GitHub Actions integration

This PR updates the Coveralls GitHub Actions integration to properly report test coverage:

1. Added LCOV formatter to generate coverage reports in a format that Coveralls can better process
2. Configured the Coveralls GitHub Action with additional parameters for parallel builds
3. Added a finish job to aggregate coverage reports from all matrix builds
4. Updated the README badges to reflect the move from Travis CI to GitHub Actions

The changes have been tested locally and all tests pass successfully.

Link to Devin run: https://app.devin.ai/sessions/368c279ca63c4496b67dcffead5c0d6f
Requested by: User

[devin-ai-integration]

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